Thermal recording apparatus

Abstract

A thermal recording apparatus for recording an information signal on the heat-sensitive recording medium in a form of visible information comprises a plurality of heat-generating resistance elements, a drive circuit for supplying selectively drive current to said heat-generating resistance elements in response to the information signal, a recording medium disposed in contact with the plurality of heat-generating resistance elements and adapted to change color upon sensing heat, means for driving the plurality of heat-generating resistance elements and the recording medium relative to each other, and a switching circuit means for inverting the direction of the drive current applied to the heat-generating resistance elements in a predetermined manner.

We claim: 
     
       1. A thermal recording apparatus comprising: a plurality of heat-generating resistance elements;   a driving circuitry adapted to supply drive current selectively to selected one(s) of said heatgenerating resistance element(s) in response to signal representing information to be recorded;   a recording medium disposed in contact with said plurality of heat-generating resistance elements and adapted to be changed in color by said selected heat-generating resistance element(s);   means for moving said plurality of heat-generating resistance elements and said recording medium relative to each other; and   switching circuit means for inverting the direction of said drive current supplid to said selected heat-generating resistance element(s) in a predetermined manner.   
     
     
       2. A thermal recording apparatus as set forth in claim 1, wherein said switching circuit means is adapted to repeatedly invert the direction of said drive current applied to said selected heat-generating resistance element(s) for every predetermined quantity of said information signal to be recorded. 
     
     
       3. A thermal recording apparatus as set forth in claim 1, wherein said switching circuit means is adapted to invert the direction of said drive current supplied to said selected heat-generating resistance elements for every predetermined time interval. 
     
     
       4. A thermal recording apparatus as set forth in claim 2, including: input terminal means for the signal representing the information to be recorded;   input means for receiving said drive current from an external current source;   inverter circuit means connected to said input terminal;   a controllable switching element connected to said input means for said drive current, switchable means for alternatively connecting a control electrode of said switching element to the outputs of said input terminal for information signal and said inverter circuit means;   a semiconductor element for responding to the conducting and the non-conducting states of said switching element to permit said drive current to flow through said heat-generating resistance elements exchangeably and selectively in one of both directions;   means connected in series to said heat-generating resistance elements and said semiconductor element for inverting said drive current; and   means connected to said input means for said information signal for changing over said connecting means and said inverter means in an interlocked manner when said information signal has attained said predetermined quantity.   
     
     
       5. A thermal recording apparatus as set forth in claim 4, wherein said switching element is composed of a transistor and said semiconductor element is composed of a bi-directional current control element. 
     
     
       6. A thermal recording apparatus as set forth in claim 1, including: input terminal means for said information signal to be recorded;   means for receiving said drive current from an external a.c. power source;   inverter circuit means connected to said input terminal means;   a switching element having a control electrode, switchable means for alternatively connecting said control electrode of said switching element to the outputs of said input terminal means and said inverter circuit means;   a semiconductor element for responding to the conducting and the non-conducting states of said switching element to permit said drive current to flow through said heat-generating resistance element exchangeably and alternatively in one of both directions; and   means connected to said input means for said drive current and adapted to change over said connecting means in dependence upon the polarities of said drive current.   
     
     
       7. A thermal recording apparatus as set forth in claim 6, wherein said switching element is composed of a transistor and said semiconductor element is composed of a bi-directional current control element.